2.
What is the distribution of K+ within the body compartments? Why is this distribution important?
3.
What are the hormones and factors that regulate plasma K+ levels? Why is this regulation important?
4.
How do the various segments of the nephron transport K+ , and how does the mechanism of K+ transport by these segments determine how much K+ is excreted in the urine?
5.
Why are the distal tubule and collecting duct so important in regulating K+ excretion?
6.
How do plasma K+ levels, aldosterone, vasopressin, tubular fluid flow rate, and acid-base balance influence K+ excretion?
7.
What is the physiological importance of calcium (Ca++) and inorganic phosphate (Pi)?
8.
How does the body maintain Ca++ and Pi homeostasis?
9.
What roles do the kidneys, intestinal tract, and bone play in maintaining plasma Ca++ and Pi levels?
10.
What hormones and factors regulate plasma Ca++ and Pi levels?
11.
What are the cellular mechanisms responsible for Ca++ and Pi reabsorption along the nephron?
12.
What hormones regulate renal Ca++ and Pi excretion by the kidneys?
13.
What is the role of the calcium-sensing receptor (CaSR)?
14.
What are some of the more common clinical disorders of Ca++ and Pi homeostasis?
15.
What is the role of the kidneys in the production of calcitriol (active form of vitamin D)?
16.
What effects do loop and thiazide diuretics have on Ca++ excretion?
Potassium (K+) is one of the most abundant cations in the body, and it is critical for many cell functions, including regulation of cell volume, regulation of intracellular pH, synthesis of DNA and protein, growth, enzyme function, resting membrane potential, and cardiac and neuromuscular activity. Despite wide fluctuations in dietary K+ intake, [K+] in cells and extracellular fluid (ECF) remains remarkably constant. Two sets of regulatory mechanisms safeguard K+ homeostasis. First, several mechanisms regulate [K+] in the ECF. Second, other mechanisms maintain the amount of K+ in the body constant by adjusting renal K+ excretion to match dietary K+ intake. It is the kidneys that regulate excretion of K+ .
Total body [K+] is 50 mEq/kg of body weight, or 3600 mEq for a 70-kg individual. Ninety-eight percent of the K+ in the body is located within cells, where the average [K+] is 150 mEq/L. High intracellular [K+] is required for many cell functions, including cell growth and division and volume regulation. Only 2% of total body [K+] is located in the ECF, where its normal concentration is approximately 4 mEq/L. A [K+] in ECF that exceeds 5.0 mEq/L constitutes hyperkalemia. Conversely, a [K+] in ECF of less than 3.5 mEq/L constitutes hypokalemia.